m/z MASS Spectrometry(MS)

MASS Spectrometry (MS)

Sample Ions Detector

Ionisation

m/z

EI ESI

APCI, FAB, MALDI, etc

M

M+H

M+Na

M+M’+H

M

fragments

Electric/magnetic field

accelerate/

circleshaped orbit

Invasive, but very sensitive (10 ^-15 -10 ^-21 mol!!)

EI (electron impact) – hard ionisation

EI

Sample holder

→ 10-20 g Heated by program, sample holding stick

Pros

1. Most of small molecules 2. Lots of fragments

3. Programmed heating, some separation

1. M+ is small, or not observable

2. Not suitable for thermally labile compounds

ESI (electrospray ionisation)– mild ionisation

Sample in

solution

MeOH, AcCN, H

O

MH

, MHsolv

, M+Na

Negative mode is also possible!

Sample inlet directly (in

solution) or coupled with LC

MS Spectrum

Under given circumstances the spectrum is relevant

to the molecule!

What do we expect?

C ₂₇ H ₄₈

M=372

Every molecule is detected separatly!!!

12

C

H

,

C

C

H

,

C

C

H

, etc

13

C has 1,1% abundance: I(M+1)/I(M)~N(C)

MS spectrum of chlorine containing molecule

MS spectrum of bromine containing molecule

Izotop ratios

Most abundant

Less abundant

Ratio

12

C

C 100 1.1 M+1

16

O

O 100 0.2 M+2

35

Cl

Cl 100 32.5 M+2

ca 3:1

79

Br

Br 100 98 M+2

ca 1:1

32

S

S 100 5 M+2

Isotope ratios if more halogens are present

Cl Cl₂ Cl3

Br

Br

Br

2

3

MS spectrum of sulphur containing molecule

C H

CH

O H

C

CH

M=58!

m/z = 120 M M (%) M+1 (%) M+2 (%) C₂H₄N₂O₄ 120,017107 100 3,15 0,84 C₂H₆N₃O₃ 120,040916 100 3,52 0,65 C₃H₁₂N₄O 120,101111 100 5,00 0,31 C₄H₁₂N₂O₂ 120,089878 100 5,36 0,52 C₆H₆N₃ 120,056172 100 7,72 0,26

C₉H₁₂ 120,093900 100 9,92 0,44

m(N)+2m(H)≠m(O) Mass defect

HRMS: High Resolution Mass Spectrum

Nominal mass

Resolution in MS

FWHM: Full width at half maximum

How much R is needed? R>30000

m/z = 120 M M (%) M+1 (%) M+2 (%)

C₂H₄N₂O₄ 120,017107 100 3,15 0,84 C₂H₆N₃O₃ 120,040916 100 3,52 0,65 C₃H₁₂N₄O 120,101111 100 5,00 0,31 C₄H₁₂N₂O₂ 120,089878 100 5,36 0,52 C₆H₆N₃ 120,056172 100 7,72 0,26

C₉H₁₂ 120,093900 100 9,92 0,44

Nominal mass

Monoisotopic mass

Homework 3

Pipobroman is an anticancer drug. Calculate its M⁺, scetch its EI MS spectrum between m/z 350-360, give explanation.

Does it have characteristic IR absorption bands? If yes, which group, what wavenumber?